2. Step 1 Eligibility (Pre-Operative Eligibility) Includes: Diagnosis and Age - Patients with tumor originally located within the posterior fossa of the brain: *Patients ≤ age 21 years with recurrent medulloblastoma (PNET) involving the brain and/or spine *Patients ≤ age 21 years with recurrent ependymoma involving the brain and/or spine *Patients ≤ age 21 years with recurrent atypical teratoid/rhabdoid tumor (AT/RT) involving the brain and/or spine.